Computer users often need to disconnect from a network and work offline, such as when traveling, working at home, or at times when the network is down. As a result, various mechanisms have been directed to caching network information on a local computer to allow the information to be accessed when the local computer is disconnected from the network. Local caching also reduces the amount of data communicated between the network servers and a client working in an offline mode. Benefits to reducing the amount of transmitted data include a reduction in the server workload, a reduction in the client's perceived latency, and an increase in available network bandwidth.
Working offline usually changes the state of the offline directory hierarchy relative to the server directory hierarchy. Changes to the directories in the hierarchies can come in the form of a file change such as a change of attributes or a data write, or in the form of a namespace change such as the creation of a new file or directory, or the deletion of a file.
Regardless of the change or changes, at some point it becomes necessary to perform some process to synchronize the offline client and server directories into a synchronized state. In a synchronized state, the two directory hierarchies have the same subdirectory structure, containing the same filenames within those directories. Also, for each file that exists in both directories, the files need to contain the same data in their data streams and have the same associated attributes, timestamps and other file system information.
However, synchronizing the cached offline items with the server file system's items (directories and files) is complex, relatively slow and has always suffered from problems. What is needed is a fast and reliable way to synchronize offline files.